SOFC Cathode Material Research Articles

Study on the effects of configuration entropy to electrochemical properties of A2BO4-type cathode materials for SOFCs

High entropy oxides are one of the research topicalities in the field of SOFC. However, the relationship between configuration entropy and the electrochemical properties of these materials is not well understood. Here, a medium entropy material (La0.2Pr0.2Nd0.2Sm0.2Eu0.2)2CuO4 ((Ln0.2)2CuO4) derived from Nd2CuO4 material is designed. It was found that increasing the configuration entropy of the A-site promotes the production of highly reactive/concentrated non-stoichiometric oxygen and increases the covalency of the Cu3d-O2p orbital. The polarization impedance of (Ln0.2)2CuO4 is 0.92 Ω cm2 at 700 °C, which is smaller than that of Nd2CuO4 (1.8 Ω cm2 at 700 °C). The peak power density of single cells NiO-YSZ|YSZ|GDC|cathode is 526 mW cm−2 at 700 °C within 60 h of stable operation at 0.5 V. First-principles calculations demonstrate that (Ln0.2)2CuO4 has lower charge transfer energy, which promotes the electronic conduction. Furthermore, the dissociation energy of adsorbed oxygen (Oad) on the surface of (Ln0.2)2CuO4 is 2.24 eV, which is smaller than that of Nd2CuO4 (2.26 eV). These results suggest that the entropy-increasing strategy can enhance the electrocatalytic performance.

Towards high performance durable ceramic fuel cells using a triple conducting perovskite cathode

To guarantee the efficient and durable operation of oxygen ion/proton-conducting ceramic fuel cells, the cathode materials need to be versatile in terms of high activity, good CO2 resistance, and matched thermal expansion behavior with electrolyte, etc. In this study, we substituted 10% Nb to the B-site of parent perovskite-BaCo0.7Fe0.2Y0.1O3-δ, to form a single-phase material with triple conducting (H+/O2-/e-) capability as a highly ORR-active cathode. The doped BaCo0.6Fe0.2Y0.1Nb0.1O3-δ (BCFYN) shows promising ORR activity due to the optimized oxygen vacancy, improved hydration capacity, and accelerated charge transfer kinetics. The reduction of thermal expansion coefficient (TEC) and enhanced CO2 resistance also facilitate the cathode durability. As a result, the area-specific resistances of BCFYN electrode at 550 °C for oxygen-ion and proton conducting symmetrical cells were only 0.106 and 0.24 Ω cm2, respectively. These results indicate that BCFYN is a highly promising cathode material for both SOFCs and PCFCs.

Alternative B-site-doped La0.6Sr0.4Co0.2Fe0.8-xMxO3 (M = Ni, Cu, Nb; x = 0, 0.1, 0.2) as innovative cathode material for LT-SOFC with enhanced charge transfer and oxygen ion diffusion

Although La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) owns a high level of maturity as a cathode material for intermediate and high-temperature SOFCs, there still exists tremendous potential for it to be employed under an efficient low-temperature working conditions. Since the charge transfer and oxygen ions diffusion act as pivotal obstacles to realizing the operation of LT-SOFCs (below 600 °C), the B-site doping elements (Ni, Cu, Nb) in commercial LSCF are selected using the first-principles calculation. Based on the theoretical findings, the novel Cu-doped La0.6Sr0.4Co0.2Fe0.8-xCuxO3 (LSCFCx, x = 0, 0.1, 0.2) cathode materials are synthesized with exploring the phase structure, valence states of the elements, and thermogravimetric properties. Among different doping elements, Cu doping could facilitate the electrochemical performance of LSCFCx cathode by the enhancement of electrons at B-site and enrichment the of oxygen vacancies. Arising from the inspiring charge transfer and the accelerating oxygen ion transportation, Cu-substitution yields superior activity than other LSCF doping elements. The polarization resistant and activation energy values for LSCFC0.2 cathode attenuates more than 71% and 35% in contrast to the undoped LSCF cathode, respectively. The maximal power density of the anode-supported single cells utilizing LSCFC0.2 cathode outputs 0.594 W∙cm‐2 at 600 °C and promotes over 41% than commercial LSCF at the same condition. These results conclusively point to a practical Cu-doping strategy for the development of highly efficient cathodes for LT-SOFCs.

Ca and Fe co-doped NdBaCo2O5+δ double perovskites as high-performance cathodes for solid oxide fuel cells

For intermediate-temperature solid oxide fuel cells (IT-SOFCs), high electrochemical catalytic activity and a suitable thermal expansion coefficient (TEC) are essential criteria. In this investigation, simultaneous Ca and Fe co-doped NdBa1-xCaxCoFeO5+δ (NBCCF, x = 0, 0.1, and 0.2) double-perovskites were prepared and investigated as SOFC cathode materials. The introduction of Ca and Fe effectively decreased the TECs and improved the oxygen reduction activity of the cathode. The average TEC of NdBa0.9Ca0.1CoFeO5+δ (NBCCF1) at 30–850 °C was 19.1 × 10−6 K−1, which is decreased by 27.1 % compared to the only Fe-doped NdBaCoFeO5+δ (NBCF). According to the distribution of relaxation time (DRT) analysis, the rate-limiting steps of the oxygen reduction reaction (ORR) include bulk diffusion and surface exchange of oxygen, and Ca doping can improve both steps. The maximum power density of the single cell with NBCCF1 as cathode reached 665 mW cm−2 at 750 °C. The polarization resistance decreased from 0.0722 to 0.0482 Ω cm2 at 800 °C. These findings indicate NBCCF1 is a viable cathode candidate for IT-SOFC.

Doping strategy on improving the overall cathodic performance of double perovskite LnBaCo2O5+δ (Ln=Pr, Gd) as potential SOFC cathode materials

A series of single-phase double perovskite Pr1-xGdxBaCo2-yFeyO5+δ (x = 0, 0.5 and 1, 0 ≤ y ≤ 1) materials were engineered through A/B site co-doping strategy to improve the mechanical, electrical and electrochemical properties as potential cathode materials for the application of intermediate solid oxide fuel cells (IT-SOFCs). The corresponding thermochemical stability, thermal expansion behavior, electrical conductivity and cathodic polarization resistance of the materials were systematically investigated. It was found that the A-site dual lanthanide doped Pr0.5Gd0.5BaCo2O5+δ (PGBCO) exhibits improved electrical conductivity, reduced thermal expansion, and comparatively low electrochemical polarization resistance versus single lanthanide double perovskite, PrBaCo2O5+δ (PBCO) and GdBaCo2O5+δ (GBCO) materials. Further investigation on the effect of B-site Fe-doping on Pr0.5Gd0.5BaCo2-yFeyO5+δ (PGBCF-y, 0 ≤ y ≤ 1) reveals that all the PGBCF-y compositions exhibit excellent chemical stability with Gd-doped ceria (GDC) at operating temperatures not higher than 1 100 °C. Besides, doping of Fe in B-site can effectively reduce the thermal expansion coefficients (TECs) of the Pr0.5Gd0.5BaCo2O5+δ ceramics at 30–1 000 °C. And the electrochemical impedance spectra (EIS) results show that the PGBCF-y|GDC| PGBCF-y symmetric cells have acceptable low area specific polarization resistances. Further examination of the cathodic polarization and characteristic capacitance from the AC impedance spectra by employing the relaxation time distribution (DRT) method demonstrated that charge transfer is the dominating sub-process for the oxygen transport through the materials.

Structural, dielectric and conductive properties of Ag substituted (La0.80Sr0.20)1-xAgxMnO3{x = 0.15 and 0.20} cathode material for SOFCs

Silver doped (La0.80Sr0.20)1-xAgxMnO3{x = 0.15 and 0.20} solid solutions has been synthesized by the use of solid state reaction method. Sample pellets has been calcined and then sintered at temperature 1400 0C and then characterized to study structural, dielectric and conductive properties. XRD analysis confirmed the single phase as well as crystalline size in nanometer of the material. In addition to this material showed tensile strain. Morphology has been studied by the use of scanning electron microscope. Density of the peroveskite has been found to be decreased with Silver substitution. Impedance analyzer has been used to determine the dielectric and conductive properties of the material which confirmed non-Debye behaviour of the material. Decrease in activation energy confirms the increases in conductivity value with Silver modification.

Electronic and ionic effects of sulphur and other acidic adsorbates on the surface of an SOFC cathode material.

The effects of sulphur adsorbates and other typical solid oxide fuel cell (SOFC) poisons on the electronic and ionic properties of an SrO-terminated (La,Sr)CoO3 (LSC) surface and on its oxygen exchange kinetics have been investigated experimentally with near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS), low energy ion scattering (LEIS) and impedance spectroscopy as well as computationally with density functional theory (DFT). The experiment shows that trace amounts of sulphur in measurement atmospheres form SO2- 4 adsorbates and strongly deactivate a pristine LSC surface. They induce a work function increase, indicating a changing surface potential and a surface dipole. DFT calculations reveal that the main participants in these charge transfer processes are not sub-surface transition metals, but surface oxygen atoms. The study further shows that sulphate adsorbates strongly affect oxygen vacancy formation energies in the LSC (sub-)surface, thus affecting defect concentrations and oxygen transport properties. To generalize these results, the investigation was extended to other acidic oxides which are technologically relevant as SOFC cathode poisons, such as CO2 and CrO3. The results unveil a clear correlation of work function changes and redistributed charge with the Smith acidity of the adsorbed oxide and clarify fundamental mechanistic details of atomic surface modifications. The impact of acidic adsorbates on various aspects of the oxygen exchange reaction rate is discussed in detail.

Tuning Cu-Content La1-xSrxNi1-yCuyO3-δ with Strontium Doping as Cobalt-Free Cathode Materials for High-Performance Anode-Supported IT-SOFCs.

Cu-content La1-xSrxNi1-yCuyO3-δ perovskites with A-site strontium doping have been tuned as cobalt-free cathode materials for high-performance anode-supported SOFCs, working at an intermediate-temperature range. All obtained oxides belong to the R-3c trigonal system, and phase transitions from the R-3c space group to a Pm-3m simple perovskite have been observed by HT-XRD studies. The substitution of lanthanum with strontium lowers the phase transition temperature, while increasing the thermal expansion coefficient (TEC) and oxygen non-stoichiometry δ of the studied materials. The thermal expansion is anisotropic, and TEC values are similar to commonly used solid electrolytes (e.g., 14.1 × 10-6 K-1 for La0.95Sr0.05Ni0.5Cu0.5O3-δ). The oxygen content of investigated compounds has been determined as a function of temperature. All studied materials are chemically compatible with GDC-10 but react with LSGM and 8YSZ electrolytes. The anode-supported SOFC with a La0.95Sr0.05Ni0.5Cu0.5O3-δ cathode presents an excellent power density of 445 mW·cm-2 at 650 °C in humidified H2. The results indicate that La1-xSrxNi1-yCuyO3-δ perovskites with strontium doping at the A-site can be qualified as promising cathode candidates for anode-supported SOFCs, yielding promising electrochemical performance in the intermediate-temperature range.

Gluing Ba0.5Sr0.5Co0.8Fe0.2O3−δ with Co3O4 as a cathode for proton-conducting solid oxide fuel cells

The Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) + Co3O4 composite material is evaluated as a cathode for proton-conducting solid oxide fuel cells (H-SOFCs), which provides a new strategy to solve the thermal mismatch problem between the cathode and electrolyte without impairing the cathode performance. BSCF is a well-known cathode material for intermediate-temperature SOFCs, but its performance for H-SOFCs is unsatisfactory. One reason for the relatively low performance is the poor contact between the BSCF cathode and the electrolyte due to the high thermal expansion of BSCF. The relatively low melting point of Co3O4 is taken in this study as an advantage to bond the BSCF cathode to the electrolyte, mitigating the poor contact problem for the BSCF with the electrolyte. Furthermore, the addition of Co3O4 promotes the catalytic activity of the BSCF cathode as demonstrated by experimental studies and first-principles calculations, leading to an impressively high performance of BSCF-based cathodes for H-SOFCs.

A heuristic approach to boost the performance and Cr poisoning tolerance of solid oxide fuel cell cathode by robust multi-doped ceria coating

Herein, highly conductive, robust, and innovative Gd and Pr multi-doped ceria (GPDC) coating, to boost the ORR kinetics and stability against Cr poisoning of the state-of-the-art La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) cathode, is reported. The GPDC coating significantly enhanced the ORR kinetics by ameliorating the surface of the LSCF cathode and showed a two-fold increment in the electrochemical performance compared to the cell with a bare LSCF cathode. The SOFC with GPDC-coated LSCF cathode showed outstanding stability at 700 °C for 500 h with a degradation rate of 0.001% h−1 in an accelerated Cr poisoning test which is attributed to the alleviation of the formation in SrCrO4. Both distributions of relaxation time-based analysis and experimental results indicate that the GPDC coating improves the ORR activity and Cr tolerance of the LSCF cathode. This study provides a comprehensive and smart strategy to tailor the surface of SOFC cathode materials to enhance performance and durability.

SOFC cathode material of La1.2Sr0.8CoO4±δ with a fibrous morphology: Preparation and electrochemical performance

Using soluble salts as metal-ion sources and polyacrylonitrile (PAN) as a polymer matrix, La1.2Sr0.8CoO4±δ cathode material with a fibrous morphology is prepared by electrostatic spinning, and microstructural characteristic of this material is investigated by field-emission scanning microscopy and X-ray diffraction. Electrochemical performance of the material in solid-oxide fuel cells is then tested. The results demonstrate that phase-pure La1.2Sr0.8CoO4±δ fibrils with tetragonal structure can be prepared from fresh silky precursors using electrospinning after annealing at high temperature. Compared to the conventional cathode material that possesses a plain granular structure, La1.2Sr0.8CoO4±δ fibrils exhibit superior electrochemical performance. At a temperature of 800 °C, the area specific resistance with this fibrous cathode is as low as 0.043 Ω cm2, and maximum power density with the corresponding single-cell is 716 mW cm−2, demonstrating the fast electrode kinetics in the O2 reduction reaction. Comparatively, the area specific resistance with the plain cathode is 0.062 Ω cm2, and the maximum power density with the corresponding single-cell is only 642 mW cm−2. Under a constant voltage load of 0.6 V at a fixed temperature of 750 °C, the power output from a single-cell with the fiber-structured cathode maintains between 615 mW cm−2 and 585 mW cm−2 even after 15 h of running time, showing a slower fading rate and a more stable electrochemical performance than the plain cathode.

Co and Hf co-doped BaFeO3 cathode with obviously enhanced catalytic activity and CO2 tolerance for solid oxide fuel cell

It is essential to develop efficient and stable cathode materials operated at intermediate temperature for the application of solid oxide fuel cell. In this work, BaFeO3–δ based perovskite oxide was used to explore the influence of Co and Hf co-doping on the catalytic activity and CO2 tolerance of SOFC cathode materials. Among the series materials, BaCo0·2Fe0.7Hf0.1O3–δ (BC2FHO) shows excellent catalytic activity and CO2 stability. The EIS measurement shows that the polarization resistance (Rp) of BC2FHO is ∼0.04 Ω cm2 at 800 °C. In the CO2 tolerance test, the Rp decreases to ∼0.0435 Ω cm2 within 1 h after removing 10% CO2. The peak power density of the single cell with BC2FHO cathode are 1010.4, 649.4, and 256.6 mW cm−2 at 800, 700, and 600 °C, respectively. And the total degradation rate of the output voltage at 700 °C is only 0.009% h−1. The significantly enhanced activity and stability are attributed to Co and Hf co-doping. The incorporation of Hf allows BaFeO3 to obtain a highly symmetrical cubic structure with increased oxygen ion transport channels, which is conducive to promote the oxygen reduction reaction. In addition, Hf-doping can also increase the acidity to make the material resistant to CO2. The incorporation of Co improves the concentration of oxygen vacancies, which makes BC2FHO show excellent electrochemical performance.

A-site doping enabled higher-oxygen-vacancy cobalt-free layered perovskite cathode for higher-performing protonic ceramic fuel cells

Cobalt-free layered perovskite as a promising mixed ionic electronic conductor cathode has shown outstanding performance in conventional oxygen-ion conducting solid oxide fuel cells (O–SOFCs), but not in next-generation proton-conducting solid oxide fuel cells (H–SOFCs) due to insufficient oxygen vacancy so far. We propose a facile A-site doping strategy to enable higher-oxygen-vacancy cobalt-free layered perovskite cathode for higher-performing protonic ceramic fuel cells at reduced temperatures. As proof of concept, two different typical A-site doping of mixed-rare-earth Nd and alkali-metal K in PrBaFe1.9Zn0.1O5+δ are chosen as potential H–SOFC cathode materials. Pr0.8Nd0.2BaFe1.9Zn0.1O5+δ (PNBFZ) and PrBa0.9K0.1Fe1.9Zn0.1O5+δ (PBKFZ) layered perovskite cathodes were synthesized using a nitrate-gel combustion method. Both PNBFZ and PBKFZ have a layered perovskite structure and are chemically compatible with protonic BaZr0.1Ce0.7Y0.2O3−δ (BZCY) electrolyte. Both Nd and K doping dramatically improve the electrical conductivities under operation temperatures. Compared with PBKFZ, PNBFZ shows a lower average thermal expansion coefficient (TEC) of 13.9✕10−6 K−1, being thermally compatible with the BZCY electrolyte without cracks. A-site doping in Fe-based layered perovskite cathodes promotes the single-cell output performance by around 100-26% at 550–700 °C, especially for the mixed-rare-earth doped PNBFZ with high peak power densities of 401–650 mW cm−2.

A SrCo0.9Ta0.1O3-δ derived medium-entropy cathode with superior CO2 poisoning tolerance for solid oxide fuel cells

The development of highly efficient and robust cathodes is crucial for intermediate temperature solid oxide fuel cells (IT-SOFC). Perovskite type SrCo0.9Ta0.1O3-δ (SCT91) is a promising cathode but its instability against CO2 limits the practical application. In this work, a new medium-entropy SrCo0.5Fe0.2Ti0.1Ta0.1Nb0.1O3-δ (SCFTTN52111) cathode is designed and evaluated. The effect of configuration entropy on electrical conductivity, physical and electrochemical properties are studied in detail. The SCFTTN52111 cathode exhibits a lower polarization resistance of 0.033 Ω cm2 at 700 °C, superior to 0.040 Ω cm2 of SCT91 parent. The higher oxygen reduction activity is attributed to its larger surface exchange coefficient and smaller particle size. More importantly, SCFTTN52111 displays outstanding stability and high CO2 tolerance, due to a more negative value of average metal-oxygen bond energy and significantly reduced surface Sr segregation. Our study provides a feasible and effective entropy engineering approach to design high-active and durable cathode materials for SOFCs.

In situ techniques reveal the true capabilities of SOFC cathode materials and their sudden degradation due to omnipresent sulfur trace impurities.

In this study, five different mixed conducting cathode materials were grown as dense thin films by pulsed laser deposition (PLD) and characterized via in situ impedance spectroscopy directly after growth inside the PLD chamber (i-PLD). This technique enables quantification of the oxygen reduction kinetics on pristine and contaminant-free mixed conducting surfaces. The measurements reveal excellent catalytic performance of all pristine materials with polarization resistances being up to two orders of magnitude lower than those previously reported in the literature. For instance, on dense La0.6Sr0.4CoO3−δ thin films, an area specific surface resistance of ∼0.2 Ω cm2 at 600 °C in synthetic air was found, while values usually >1 Ω cm2 are measured in conventional ex situ measurement setups. While surfaces after i-PLD measurements were very clean, ambient pressure X-ray photoelectron spectroscopy (AP-XPS) measurements found that all samples measured in other setups were contaminated with sulfate adsorbates. In situ impedance spectroscopy during AP-XPS revealed that already trace amounts of sulfur present in high purity gases accumulate quickly on pristine surfaces and lead to strongly increased surface polarization resistances, even before the formation of a SrSO4 secondary phase. Accordingly, the inherent excellent catalytic properties of this important class of materials were often inaccessible so far. As a proof of concept, the fast kinetics observed on sulfate-free surfaces were also realized in ex situ measurements with a gas purification setup and further reduces the sulfur concentration in the high purity gas.

Investigating oxygen reduction pathways on pristine SOFC cathode surfaces by in situ PLD impedance spectroscopy.

The oxygen exchange reaction mechanism on truly pristine surfaces of SOFC cathode materials (La0.6Sr0.4CoO3−δ = LSC, La0.6Sr0.4FeO3−δ = LSF, (La0.6Sr0.4)0.98Pt0.02FeO3−δ = Pt:LSF, SrTi0.3Fe0.7O3−δ = STF, Pr0.1Ce0.9O2−δ = PCO and La0.6Sr0.4MnO3−δ = LSM) was investigated employing in situ impedance spectroscopy during pulsed laser deposition (i-PLD) over a wide temperature and p(O2) range. Besides demonstrating the often astonishing catalytic capabilities of the materials, it is possible to discuss the oxygen exchange reaction mechanism based on experiments on clean surfaces unaltered by external degradation processes. All investigated materials with at least moderate ionic conductivity (i.e. all except LSM) exhibit polarization resistances with very similar p(O2)- and T-dependences, mostly differing only in absolute value. In combination with non-equilibrium measurements under polarization and defect chemical model calculations, these results elucidate several aspects of the oxygen exchange reaction mechanism and refine the understanding of the role oxygen vacancies and electronic charge carriers play in the oxygen exchange reaction. It was found that a major part of the effective activation energy of the surface exchange reaction, which is observed during equilibrium measurements, originates from thermally activated charge carrier concentrations. Electrode polarization was therefore used to control defect concentrations and to extract concentration amended activation energies, which prove to be drastically different for oxygen incorporation and evolution (0.26 vs. 2.05 eV for LSF).

Ca-doped PrBa1-xCaxCoCuO5+δ (x = 0–0.2) as cathode materials for solid oxide fuel cells

Ca-doped perovskite oxides PrBa1-xCaxCoCuO5+δ (PBCCCO, x = 0–0.2) were prepared and investigated as SOFC cathode materials. PBCCCO samples are single perovskite structure with P4/mmm space group. Pr, Cu and Co ions in PBCCCO samples exist in the form of Pr3+/Pr4+, Cu2+/Cu+ and Co3+/Co4+ multi-valence states. The average TECs of PBCCCO samples were reduced from 17.4 × 10−6 K−1 (x = 0) to 16.7 × 10−6 (x = 0.1) and 16.1 × 10−6 K−1 (x = 0.2) whin RT-900°С. The electrical conductivity and electrochemical catalytic activity of PBCCCO perovskites was enhanced obviously by Ca doping. The ASR values decreased by 60.1% (@650 °C), 68.9% (@700 °C), 71.0% (@750 °C) and 72.8% (@800 °C) respectively when Ca doping content increased from x = 0 to 0.2. These results suggest PBCCCO sample with Ca doing content x = 0.2 can be a promising cathode for IT-SOFC.

Influence of Ba2+ substitution on Structural, Dielectric, Thermal and Electrical behavior of La1-xBaxCo0.50 Fe0.50O3 {0.10≤ x≤ 0.40} Cathode for SOFC

La1-xBaxCo0.50Fe0.50 O3; {0.10≤ x≤ 0.40} perovskite ceramics is prepared by solid-state reaction method. The as-prepared samples are characterized by X-ray diffraction, scanning electron microscope, dilatometer, thermogravimetric analyzer (TGA) and impedance spectrometer. Samples are well crystallized in single phase and the crystal structure is found to be rhombohedral. Grains are non uniform and size of the grains is decreasing with Ba substitution. Density of the material is measured by Archimedes principle. At high temperature, reduction of cobalt and iron takes place. Thermal expansion coefficients for x = 0.10 and 0.40 at 200 °C - 800 °C temperature are 13.4 ×10-6 °C- 1 and 11.8×10-6 °C-1 respectively. Dielectric analysis shows that as prepared samples obey non-Debye relaxation behavior. The maximum value of the conductivity is 136.32 Scm-1 for x = 0.10 and 168.60 Scm-1 for x = 0.40. Activation energies are found to be 0.20 eV and 0.17 eV for x = 0.10 and 0.40 respectively. Electrical conductivity is greater than 100 Scm-1 which suggests it to be a suitable cathode material for SOFCs.

Copper doped SrFe0.9-Cu W0.1O3- (x = 0–0.3) perovskites as cathode materials for IT-SOFCs

Cu doped SrFe0.9-xCuxW0.1O3-δ (x = 0, 0.1, 0.2 and 0.3) perovskites were investigated as SOFC cathode materials. The effects of Cu doping on properties of SFCW samples were studied systematically. The oxygen content (3-δ) decreased by Cu doping, which leading to the decrement of electrical conductivity and the increment of TECs of SFCW samples. The ASR first decreases with x from 0 to 0.2 and then it increases when x up to 0.3. The ASR values are 0.161, 0.134, 0.102 and 0.117 Ω cm2 at 800 °C for SFCW samples with x = 0, 0.1, 0.2 and 0.3, respectively. The corresponding activation energy are 0.90, 0.88, 0.78 and 0.86 eV. The lowest ASR and activation energy for ORR of SFCW2 is a result from the joint effects of electrical conductivity, oxygen vacancy concentration and thermal expansion caused by Cu doping. The research results obtained in this study suggesting SFCW2 is a good cathode candidate for SOFC.

Analysis of Performance Losses and Degradation Mechanism in Porous La2-X NiTiO6-δ:YSZ Electrodes.

The electrode performance and degradation of 1:1 La2−xNiTiO6−δ:YSZ composites (x = 0, 0.2) has been investigated to evaluate their potential use as SOFC cathode materials by combining electrochemical impedance spectroscopy in symmetrical cell configuration under ambient air at 1173 K, XRD, electron microscopy and image processing studies. The polarisation resistance values increase notably, i.e., 0.035 and 0.058 Ωcm2 h−1 for x = 0 and 0.2 samples, respectively, after 300 h under these demanding conditions. Comparing the XRD patterns of the initial samples and after long-term exposure to high temperature, the perovskite structure is retained, although La2Zr2O7 and NiO appear as secondary phases accompanied by peak broadening, suggesting amorphization or reduction of the crystalline domains. SEM and TEM studies confirm the ex-solution of NiO with time in both phases and also prove these phases are prone to disorder. From these results, degradation in La2−xNiTiO6−δ:YSZ electrodes is due to the formation of La2Zr2O7 at the electrode–electrolyte interface and the ex-solution of NiO, which in turn results in the progressive structural amorphization of La18NiTiO6−δ phases. Both secondary phases constitute a non-conductive physical barrier that would hinder the ionic diffusion at the La2−xNiTiO6−δ:YSZ interface and oxygen access to surface active area.